Taper taps for pipe threads made of hard material

ABSTRACT

A high durability taper tap for pipe threads which can cut threads in a pipe made of hard materials having hardness of approximately 50 HRC. The sum Σγ of the width angle of cutters is large, approximately 130°, thereby achieving high strength and rigidity are achieved. Since rake angle of the cutting edge α is approximately −20°, cutter angle β defined by the rake face and the peripheral relief becomes more than 90° so that the strength and rigidity of a cutting edge are enhanced. In addition, since a taper of the bottom of flutes is in a ratio of 1/16, approximately equal to that of the thread portion, the rake angle α of all of the cutting edges  6  is uniform so that all of the cutting edges can equally cut the threads. Further, the diameter Df of the bottom of the flutes of the top end portion is approximately 60% of the smaller end of the thread portion, which is larger than that of the common tapping tool. Owing to this configuration, the taper tap for pipe threads having high strength, rigidity and hard wearing property can be achieved.

FIELD OF THE INVENTION

This invention relates to a taper tap for pipe threads for cuttingfemale threads, and more specifically, to a high durability taper tapfor pipe threads which can cut female threads in a pipe having hardnessof approximately more than 50 Rockwell C scales Hardness (HRC).

BACKGROUND OF THE INVENTION

A taper tap for pipe threads (hereinafter referred to as a “pipe tapertap”) is a kind of hand taps and is used for cutting tapered female pipethreads for achieving an air tightness of the threads at the connectingportion of pipes, pipe components or fluid apparatuses. The pipe tapertap is different from a common tapping tool for forming trianglethreads, for instance, in some respects. The main differences betweenthese two are as follows. First, the pipe taper tap cuts the pipethreads by the thread portion of the tap tapered in a ratio of 1/16 inorder to taper the pipe threads in a ratio of 1/16, while the commontapping tool cuts the threads only by the chamfer. Second, the pipetaper tap cuts the threads not only by the crest but also by the root ofthe thread in order to improve the air tightness of the pipe thread,while the common tapping tool does not cut the threads by the root ofthe thread.

As described above, since the cutting area of the pipe taper tap islarger than that of a common tapping tool, the cutting resistance of thepipe taper tap is larger than that of the common tapping tool.Therefore, it is impossible to cut threads in a pipe made of a hardmaterial, such as the one after a heat treatment having hardness of 50HRC or more, by using a pipe taper tap.

However, sometimes a heat treatment is mistakenly conducted on thematerial to be tapped before cutting female threads therein. Since sucha material becomes hard after the heat treatment, the body of the pipetaper tap is crimped, broken, chipped or abraded in an early stage ofuse by merely cutting threads in one or two holes by the pipe taper tap.In such an event, the material after the heat treatment has to beabandoned or otherwise conducted an electrical discharge machiningprocess on the material before cutting female threads therein. However,it is difficult to accurately cut threads after the electrical dischargemachining. In addition, it takes more than several ten hours to conductthe overall process.

SUMMARY OF THE INVENTION

The present invention was made to solve the above described problems byproviding a highly durable pipe taper tap for cutting threads in a pipemade of a hard material which is able to form female threads in a pipehaving hardness of approximately 50 HRC or more.

In order to achieve the above object, the first invention of the pipetaper tap for a hard material is to form female threads in a pipe madeof hard material, wherein a sum of a width angle of each cutter is setapproximately from 110° to 150°, a rake angle of the cutting edge is setapproximately from −25° to −10°, a diameter of top end portion at thebottom of the flute is set approximately from 58% to 68% of a diameterof the smaller end of the thread portion, and a taper ratio at thebottom of the flute is set approximately from 1/21 to 1/11.

According to the pipe taper tap of the first invention for cuttingthreads in a pipe made of a hard material, the sum of the width angle ofthe cutter is set approximately from 110° to 150°. The larger the sum ofthe width angle of the cutters, the broader it becomes the width of eachof the cutters, and accordingly, the chipping or breaking of the threadportions of the cutter are reduced. On the other hand, if the width ofthe cutter becomes broader, the contacting area between the tap and thematerial to be cut becomes larger, causing not only grating sounds whencutting but also a large cutting resistance, which makes the cuttingitself difficult. Therefore, in the present invention, taking intoconsideration of these factors, the sum of the width angle of thecutters is determined to be approximately from 110° to 150°.

The rake angle of the cutting edge is set approximately from −25° to−10°. The smaller the rake angle of the cutting edge (larger in minusvalues), the larger it becomes the cutter angle defined by the rake faceand the peripheral relief, thereby improving the strength and rigidityof the cutting edge, which is able to prevent the breaking or chippingof the cutters. On the other hand, the larger the cutter angle, thelarger it becomes the cutting resistance. The taper tap must cut thepipe threads not only at the crest but also at the root of the thread.Therefore, in order to improve the strength of the cutter, the rakeangle of the cutting edge is set approximately from −25° to −10° bytaking into consideration of these factors.

A diameter of the bottom of flutes at the top end portion is setapproximately from 58% to 68% of a diameter of the smaller end potion ofthe thread portion and is formed larger than that of a common tappingtool. Therefore, the strength of the tap is improved to that extent andthe tap is prevented from being broken. If the diameter of the bottom ofthe flute at the top end portion is formed larger, the sectional area ofthe flute becomes smaller and consequently chip packing tends to becaused. However, as explained above, since the rake angle of the cuttingedge is set approximately from −25° to −10°, the chips are cut inrelatively small pieces in a sheared shape. Therefore, even if thesectional area of the flute is small, chip packing can be effectivelyavoided.

Further, the bottom of the flute is tapered approximately in a ratiofrom 1/21 to 1/11. Since taper at the thread portion is set in a ratioof 1/16 according to the Japanese Industrial Standard (JIS)specification, the rake angle of the cutting edge from the smaller endto the larger end can be set approximately equally. Since the pipe tapertap of the present invention cuts the pipe threads by using all of thecutters, by setting the rake angle of all of the cutting edgesapproximately the same, all of the cutters can cut the pipe threads inthe same manner.

The pipe taper tap of the second invention for cutting threads in a pipemade of a hard material comprises the taper tap for a hard pipe of thefirst invention, wherein the number of flutes provided therewith is fiveor more.

The pipe taper tap of the second invention for cutting threads in a pipemade of a hard material functions in a manner equivalent to the pipetaper tap of the first invention. In addition, the sectional area of theflute for ejecting the chips is set small by forming the diameter of thebottom of the flutes within approximately from 58% to 68% of thediameter of the smaller end of the thread portion. However, since thenumber of the flutes provided with the taper tap is large, such as fiveor more, ejection of the chips is smoothly performed, thereby avoidingan increase of the cutting resistance because of jamming of chips. Also,by providing five or more flutes with the taper tap, the cutting amountper cutting edge becomes small, thereby decreasing a cutting load foreach cutting edge.

The pipe taper tap of the third invention for cutting threads in a pipemade of a hard material comprises the pipe taper tap of the first orsecond invention, wherein the rake angle of the cutters is setapproximately −20°, the diameter of the bottom of the flute at the topend of the tap is set approximately 60% of the thread portion, thenumber of the flutes is five and the taper of the bottom of the flutesis made approximately identical to that of the thread portion. Byforming the taper at the bottom of the flute approximately equal to thatof the thread portion, the rake angle of the cutting edges from thesmall end to the large end may be set approximately the same. Therefore,it becomes possible for all of the cutting edges to perform the cuttingin the same manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of the pipe taper tap for cutting threads in apipe made of a hard material showing an embodiment of the presentinvention.

FIG. 2 is a partial expanded view of the pipe taper tap shown in FIG. 1viewed from the direction indicated by the arrow A in FIG. 1.

FIG. 3 is a table comparing the durability of the pipe taper tap of theembodiment of the present invention with durability of the conventionalexamples (1) and (2) of pipe taper taps.

EXPLANATION OF REFERENCE CHARACTERS

1 Pipe taper tap for threads of hard material

1 a Top end portion

2 Thread portion

2 a Chamfer

2 b Complete thread portion

4 Flute land cutting edge

8 Cutting face

α Rake angle

β Cutter angle

γ Width angle of cutters

D Outside diameter of smaller end of thread

Df Diameter of bottom of flute at top end portion

O Axial center

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred embodiment of the present invention is explained withreference to the attached drawings.

FIG. 1 is a front view of the taper tap for pipe threads made of a hardmaterial for showing an embodiment of the present invention, namely ataper tap for pipes made of a hard material (hereinafter merely referredto as a “pipe taper tap”).

The pipe taper tap 1 is comprised of a thread portion 2 at the side ofthe top end 1 a and a shank portion 3 at the side of the back endportion. A chamfer portion 2 a having two and a half crests is providedat the top end of the thread portion 2. A complete thread portion 2 btapered in a ratio of 1/16 is provided at the back end of the chamferportion 2 a. Here, a taper ratio 1/16 is defined by a ratio between avertical length “1” and a horizontal length “16” as shown in FIG. 1. Thecomplete thread portion 2 b is formed continuously with the chamfer 2 a.Five straight flutes for ejecting the chips are provided at the threadportion 2 in the axial direction of the pipe taper tap 1. At an outersurface of the thread portion 2, each flute 4 is evenly located with aninterval of about 72°. The bottom of the flute is tapered in a ratio of1/16, which is the same as that of the complete thread portion 2 b.

FIG. 2 is a partial expanded view of the pipe taper tap 1 as shown inFIG. 1 viewed from the direction indicated by the arrow A of FIG. 1. Asshown in FIG. 2, the thread portion 2 of the taper tap 1 are dividedinto five lands 5 by five flutes 4. The width of each land 5 (width ofthe cutter) is equal to each other. The sum the central angle γ (cutterwidth angle) Σγ is set to approximately 130°. A cutting edge 6 isprovided at the end portion of each land 5. The rake angle α of thecutting edge 6 is set at approximately −20°. Further, the diameter Df ofthe bottom of the flutes at the top end portion 1 a is formed such thatthe ratio Rd (%) with respect to the diameter D at the smaller end ofthe thread portion 2, namely (Df/D)×100, is approximately 60%. Thesurface of the thread portion 2 is coated by titanium carbon nitride(TiCN). The broken line 7 of FIG. 2 shows the root of the thread.

Since the pipe taper tap 1 is formed of a super fine and hard alloycoated by the titanium carbon nitride (TiCN), it possess an excellenthard wearing properties against a hard material to be cut. Further,although five flutes are provided with the tap, the sum of the widthangle Σγ of the cutters is relatively largely set, approximately 130°,high strength and rigidity of the tap are achieved by the increasedwidth of each cutter. By this arrangement, chipping or breaking of thethread portion 2 is prevented. The broader the width of each cutter, thelarger it becomes the contacting area between the tap and the materialto be cut, causing grating sounds in the course of cutting as well asincreasing the cutting resistance. Taking these factors intoconsideration, the sum of the angle of the width of cutters Σγ is set toapproximately 130°.

Since the rake angle α of the cutting edge 6 is set at approximately−20°, the cutter angle β defined by the cutting face 8 and theperipheral relief 9 becomes greater than 90°. Therefore, the strengthand rigidity of the cutting edge 6 is improved and accordingly, breakingor chipping of the cutter is prevented. In addition, since the taper atthe bottom of the flute 4 is set in the ratio of 1/16 which is the sametaper ratio as that of the thread portion 2, the rake angle α of thecutting edge 6 from the smaller end to the larger end of the threadportion 2 becomes equal. Since the pipe taper tap 1 cuts the threads byall of the cutting edges 6, the rake angle α of all of the cutting edges6 is set equal to each other so that all of the cutting edges 6 canequally cut the threads.

As described above, if the cutter angle β becomes large, the strengthand rigidity of the cutting edge 6 are improved, on the other hand, thecutting resistance becomes large. Therefore, it becomes difficult to cutthe threads. In addition, the pipe taper tap 1 needs to cut the threadsby the root 7 of the thread. Therefore, taking these factors intoconsideration, the rake angle α of the cutting edge 6 is set toapproximately −20°.

The diameter Df of the bottom of the flute of the top end portion 1 a ofthe pipe taper tap 1 is set approximately 60% of the diameter D of thesmaller end of the thread portion 2. The diameter Df is set larger thanthat of the common tapping tool. Therefore, the strength and rigidity ofthe tap is improved and the pipe taper tap 1 is prevented from beingbroken to that extent.

The larger the ratio of the diameter Df of the bottom of the flutes ofthe top end portion la relative to the diameter D of the smaller end ofthe thread portion 2, the smaller it becomes the sectional area of theflutes 4, thereby causing chip packing in the flutes 4. However, asdescribed in the foregoing, in the present invention, since the rakeangle α is approximately −20°, the chips are cut into relatively smallpieces in a sheared shape. In addition, since the number of the flutes 4provided for ejecting the chips is five, which is larger than that ofthe common tapping tool, the cutting chips are ejected smoothly and thechip jamming is effectively prevented. Also, by providing five of theflutes 4, which is larger in number than that of the common tappingtool, the cutting amount of each cutter of the chamfer 2 a becomes smalland accordingly the cutting load against each cutter 6 at cutting isreduced.

FIG. 3 shows the comparison of the durability of the pipe taper tapswhen conducting cutting process of a hard material having a hardness ofapproximately 50 HRC by using the pipe taper tap 1 of the presentinvention and the conventional pipe taper taps (1) and (2). As shown inFIG. 3, the conventional pipe taper taps (1) and (2) were damaged andbecome unusable by cutting female threads for only one or two holes inthe pipe made of a hard material having hardness of 54.0 HRC. However,the pipe taper tap 1 of the present invention was able to cut threads in35 holes in the pipe made of a hard material having hardness of 55.0 HRCand 56.0 HRC, and in 50 holes or more made of a hard material havinghardness of 54.0 HRC.

According to the pipe taper tap 1 of the embodiment of the presentinvention, excellent strength, rigidity and hard wearing property areachieved and the increase of the cutting resistance caused by chippacking is prevented. Therefore, it becomes possible to cut highlyaccurate pipe threads made of a hard material, such as a material to becut after a heat treatment, having hardness of, for instance,approximately 50 HRC or more while maintaining a sufficient durability.

Foregoing is the explanation of the present invention based on theembodiment as described above. However, the present invention is notlimited to the above described embodiment. It is obvious that variousmodifications can be made within the scope and gist of the presentinvention. For example, the taper tap of the present invention is notlimited to the application of forming threads on the pipes but can beused in forming threads on mechanical components or bodies.

According to the embodiment of the present invention, the sum of thewidth angle of the cutter Σγ is set approximately 130°, the rake angle αof the cutting edge 6 is set approximately −20°, the diameter Df of thebottom of flutes at the top end portion is set approximately 60% of thediameter D of the smaller end of the thread portion 2, the number of theflutes 4 for ejecting the chips is five and the taper of the bottom ofthe tap is set approximately equal to the taper of the thread portion 2.However, the embodiment of the present invention is not limited to thesevalues. The taper tap of the present invention can be produced by, forinstance, setting the sum of the width of the cutter Σγ to approximatelyin a range from 110° to 150°, the rake angle α of the cutting edge 6 ina range approximately from −10° to −25°, the diameter Df of the bottomof the flute at the top end portion 1 a to approximately in a range from58% to 68% of the diameter D of the smaller end of the thread portion 2and the number of the flutes 4 for ejecting chips five or more, and thetaper of the bottom approximately from 1/21 to 1/11. By setting each ofthe values properly depending upon the taper female threads to be cut,the pipe taper tap having a sufficient durability against a hardmaterial having hardness of approximately more than 50 HRC for practicaluse can be achieved.

According to the pipe taper tap of the first invention for cuttingthreads in a pipe made of a hard material, by setting up the values ofthe sum of width angle of cutters, the rake angle of the cutting edges,the diameter of the bottom of the flute at the top end of the tap andthe taper at the bottom of the flute within the predetermined rangenoted above, the pipe taper tap having a sufficient durability forcutting threads in a pipe made of a hard material, such as a materialafter a heat treatment having hardness of approximately more than 50HRC, can be produced.

According to the pipe taper tap of the second invention for cuttingthreads in a pipe made of a hard material, in addition to the effect ofthe first invention above, the ejection of the chips is smoothlyconducted so that the increase of cutting resistance owing to the chipjamming is avoided by increasing the number of the flutes up to five ormore. Further, by providing five or more flutes, the load against eachcutting edge is reduced to improve the durability of the cutters byreducing the cutting amount of each cutter.

According to the pipe taper tap of the third invention for cuttingthreads in a pipe made of a hard material, in addition to the effects ofthe first and second invention noted above, the durability of the pipetaper tap for cutting threads made of a hard material is furtherimproved by setting the rake angle of the cutting edge to approximately−20°, the diameter of the bottom of the top end portion to approximately60% of that of the smaller end of the thread portion, the number of theflutes at five, and the taper of the bottom of the flutes approximatelyequal to that of the thread portion.

What is claimed is:
 1. A taper tap for pipe threads for cutting femalethreads made of hard material, wherein: a sum of a width angle ofcutters is in a range approximately from 110° to 150°, a rake angle of acutting edge is in a range approximately from −25° to −10°, a diameterof bottom of flutes at a top end portion is in a range approximatelyfrom 58% to 68% of a diameter of a smaller end of a thread portion, anda taper ratio of the bottom of the flutes is in a range approximatelyfrom 1/21 to 1/11.
 2. A taper tap for pipe threads for cutting femalethreads made of hard material as described in claim 1, wherein thenumber of the flutes is five or more.
 3. A taper tap for pipe threadsfor cutting female threads made of hard material as described in claim1, wherein the rake angle of the cutting edge is approximately −20°, thediameter of the bottom of the flutes at the top end portion isapproximately 60% of the smaller end of the thread portion, the numberof the flutes is five and the taper ratio of the bottom of the flutes isapproximately equal to that of the thread portion.
 4. A taper tap forpipe threads for cutting female threads made of hard material asdescribed in claim 2, wherein the rake angle of the cutting edge isapproximately −20°, the diameter of the bottom of the flutes at the topend portion is approximately 60% of the smaller end of the threadportion, the number of the flutes is five and the taper ratio of thebottom of the flutes is approximately equal to that of the threadportion.